Radar detectors have been known for some considerable time. Police radar devices that are used in the detection and measuring the speed of moving vehicles, and also intrusion and zone security devices that are used on buildings, operate in various frequency bands, often depending on the country in which they are operating. For example, in North America it is common for police devices to operate in the X band, at 10.525 gHz, and the K band at 24.150 gHz. In Europe, however, police devices may operate in very different bands.
Radar detectors have been developed for a variety of purposes and are subject to laws in various countries concerning suppression of their own emissions, since such emissions are undesirable -- especially in causing interference with the operation of other devices.
Detectors which are sensitive over broad bands of radar frequencies and sensitive to frequencies in more than one band, may cause special problems in this regard. Examples of such devices are described U.S. Pat. No. 4,630,054 issued Dec. 16th 1986 to Martinson, and in copending applications Nos. 242,540 and 242,533, each in the name of Martinson, each filed of even date herewith.
The reasons for the special problems are two-fold. Firstly, if a single horn antenna is used to pick up a broad band or several bands of frequencies, a large amount of filtering is required. Secondly, where several bands are to be monitored, a plurality of local oscillators may be used, all of which have emissions which must be shielded.
The problem is not so acute if a horn antenna is used which has a cutoff frequency above that of the local oscillators.
The present invention aims to provide a radar detection device capable of detecting frequencies in more than one frequency band, and having improved characteristics regarding microwave local oscillator leakage therefrom.